Method of embedding of an image with a color transform

ABSTRACT

The method comprises the generation of a deteriorated image associated with a first bit rate and of a deteriorated color transform associated with a second bit rate, an evaluation of a first distortion by comparison of the image with a first test image obtained by the application of the color transform to the deteriorated image, and of a second distortion by comparison of the image with a second test image obtained by the application of the deteriorated color transform to the image, and the determination of a final conjoint bit rate associated with a best trade-off between a conjoint bit rate (R=R1+R2) and a global distortion (dE=dE1+DE2). The optimized deteriorated image and the optimized deteriorated color transform are then embedded based on this conjoint bit rate.

TECHNICAL FIELD

The invention concerns a method and a system for embedding a colortransform into a color image while optimizing bit depth and distortionof these data in order to transmit or store them together by taking thebest advantage of the transmission or storing capabilities.

BACKGROUND ART

When transmitting images from an emitter (as a server) to a terminal (asa gateway), or when storing images on a storage device, transmittingand/or storing a color transform together with these images is sometimesrequired. Color transforms need to be applied to images, videos or partsof images, notably when the color coordinates representing colors inthese images need to be adapted to another color encoding standard(colorimetric color management), to another color gamut (color gamutmapping), to another viewing conditions (color appearance) or to anotherartistic intent (color grading). A color transform can modify the hue,the saturation, the white balance, the black value, the contrast, thewhite level, or other aspects of an image. If such a color transform isnot inherently available at the place (ex. gateway) where the imagesshould be color transformed, the color transform need to be transmittedto this place, notably together with the images to be transformed. Inthe following, this place is called terminal. Such a terminal may be forinstance a gateway, a TV set, a tablet or a smartphone. Images andrelated color transforms are often from the same origin, i.e. from thesame emitter. For example, a video on demand service provides images anda related color transform that both are transmitted to a terminal wherethe color transform is applied to the images before being displayed. Inanother example, images are exchanged between different post-productionfacilities. Each image has an associated color transform adapted todisplay it on a given reference display device having its own colorcharacteristics.

When images and color transforms have to be transmitted together to aterminal, or stored on a storage device, means adapted for theirtransmission (data channels, files) or storage and sufficient capacity(channel data rate, file system size) are required. This inventionaddresses a series of situations where the use of color transforms isnormally prohibited. In a first situation, an image transmission channelis not adapted to transmit color transform. For example, in a HDMIinterface, videos and various metadata can be transmitted, but thespecification of the HDMI standard does not include the notion of acolor transform. In a second situation, a storage system is not adaptedto store color transforms. For example, a video asset management systemfor video production or at home in a home network does not include thenotion of color transform, i.e. video images can be stored in files andretrieved, but no color transform can be stored together with thesevideos. In a third situation, a proprietary, open system for storage andtransmission of videos comprises means implemented to store and totransmit color transforms together with videos, but, for the reason ofdisc storage shortage and/or limited bandwidth of transmission channels,the storage and/or transmission of color transforms is prohibited.

In a situation of limited bandwidth for transmission of video images orof limited storage capacity for video images, several methods are knownto compress the data representing these images in order to match theselimitations. In order to control the quality of the received or storedimages, the so-called rate-distortion principle is generally used thatrelates an increasing data rate (less compression) with a decreasingdistortion (better quality). It is known how to apply rate distortiontheory to efficiently compress images and videos. For example, A. Ortegagives an introduction in his article entitled “Rate-distortion methodsfor image and video compression” published in the Signal ProcessingMagazine of the IEEE, volume 15, issue 6, in November 1998.

Compression and transmission of color transforms is a newer field. Acolor transform can be represented by a Color Look Up Table (CLUT), by asplines-based model, by a Gain-Offset-Gamma (GOG) model or by any otherparametric model. For a CLUT for example, the quality of the datarepresenting the color transform can be controlled by the number of CLUTentries. The larger is the number of entries, i.e. the larger is therate of data, the lower are the approximations of the CLUT, i.e. thelower is the distortion of these data.

There are known methods for image compression employing a colortransform. For example, Marpe et al. propose in their publicationentitled “AN ADAPTIVE COLOR TRANSFORM APPROACH AND ITS APPLICATION IN4:4:4 VIDEO CODING” published in the Proc. 14th European SignalProcessing Conference (EUSIPCO 2006), Florence, Italy, September 2006, amethod to choose one color transform of an image out of a set of givencolor transforms such that compression of this image yields best ratewith minimum distortion is disclosed. In this article, the colortransform is applied before image compression. Practically, the index ofthe chosen color transform would be needed to be stored or transmittedin order to allow correct decoding of the compressed image.

This invention presents a specific method to embed a color transforminto an image or a video in a context where the color transform isapplied after image compression and decoding.

Known methods exist for embedding data into images, for instance datahiding techniques such as watermarking. These methods are usually usedfor copy and copyright protection. The aim of image watermarking is toembed, in a secure way, a robust and not perceptive message (such asGaussian noise) in an image. Even if, in such methods, the data insertedin the compressed images may be themselves compressed, there is norelationship between the compression of images and the compression ofthe data.

SUMMARY OF INVENTION

This invention aims at embedding data representing a color transforminto the images that have to be transformed while controlling globallythe distortion generated by both compressions, i.e. compression of dataand compression of images.

When looking at conjoint compression and transmission of images andcolor transforms from a server to a terminal, two specificrate-distortion characteristics can be observed:

the quality (distortion) of color transforms influences the quality(distortion) of the images since each color transform is applied to theimages by the terminal;

the data rate required for the color transforms influences the qualityof the images, too, since the color transforms are embedded into theimage.

It is an artistic decision in content creation, how many colortransforms are associated to how many images.

For this purpose, a first aspect of the invention provides a method ofembedding of at least one original image with at least one originalcolor transform, comprising:

from at least said original image, a generation of a deteriorated imageassociated with a first bit rate,

from at least said original color transform, a generation of adeteriorated color transform associated with a second bit rate,

an application of said original color transform to said deterioratedimage resulting in a first test image,

an application of said deteriorated color transform to said originalimage resulting in a second test image,

an evaluation of a first distortion by comparison of the first testimage with the original image,

an evaluation of a second distortion by comparison of the second testimage with the original image,

an evaluation of a conjoint bit rate from a summation of the first bitrate with the second bit rate,

an evaluation of a global distortion from a weighted summation of thefirst distortion with the second distortion,

if a predetermined trade-off between said conjoint bit rate and saidglobal distortion is met, then determining the final conjoint bit rateassociated with the best trade-off, if said predetermined trade-off isnot met, then choosing new values of said first bit rate and/or saidsecond bit rate such that a new conjoint bit rate evaluated from asummation of this new first bit rate with the new second bit rate isinferior to the previous conjoint bit rate, and going to another loop ofsteps above with said new first bit rate and said new second bit rate,

as soon as said final conjoint bit rate associated with said besttrade-off is determined, inferring the values of the final first bitrate and of the final second bit rate the summation of which correspondsto said final conjoint bit rate in a previous loop of the steps above,and embedding the deteriorated image associated with this final firstbit rate in said previous loop with the deteriorated color transformassociated with this final second bit rate in the same previous loop.

For this purpose, a second aspect of the invention provides a method ofembedding at least one original image with at least one original colortransform, comprising:

A/ generation, from at least said one original image, of a deterioratedimage associated with a first bit rate,

B/ generation, from at least said one original color transform, of adeteriorated color transform associated with a second bit rate,

C/ application of said at least one original color transform to saiddeteriorated image to obtain a first test image,

D/ application of said deteriorated color transform to said originalimage to obtain a second test image,

E/ obtaining a first distortion by comparison of the first test imagewith the original image,

F/ obtaining a second distortion by comparison of the second test imagewith the original image,

G/ obtaining a conjoint bit rate from a summation of the first bit ratewith the second bit rate,

H/ obtaining a global distortion from a summation of the firstdistortion with the second distortion, said summation being optionallyweighted,

then, a tradeoff between the conjoint bit rate and the global distortionbeing determined,

in the case where said trade-off is met, determining a final conjointbit rate associated with said trade-off,

otherwise in the case where said trade-off is not met, selecting newvalues of said first bit rate and/or said second bit rate such that anew conjoint bit rate obtained from a summation of said new first bitrate, if any, or previous first bit rate, if no new first bit rate isselected, with said new second bit rate, if any, or previous second bitrate, if no new second bit rate is selected, is inferior to the previousconjoint bit rate, and repeating a loop of steps A/ to H/ with said newfirst bit rate and/or said new second bit rate,

when said final conjoint bit rate associated with said trade-off isdetermined, inferring the values of the final first bit rate and of thefinal second bit rate such that the summation of the final first bitrate and of the final second bit rate corresponds to said final conjointbit rate from a previous loop of steps A/ to H/, and embedding the atleast one deteriorated image associated with said final first bit ratefrom said previous loop with the deteriorated color transform associatedwith said final second bit rate from the same previous loop.

The original color transform is adapted to transform the colors of theoriginal image. Such colors are generally encoded into M colorcoordinates C(1) . . . C(M), each color coordinate being for instanceexpressed in N bits. If such an image comprises K pixels, the bit rateassociated with the original image is then K×M×N=R₀1.

The original color transform is generally represented by a color lookuptable—CLUT—having P entries, where each entry has for instance a bitrate of Q bits. Then, the bit rate associated with the original colortransform is then P×M×Q=R₀2.

Preferably, said color transforms are Color Look Up Tables (CLUT).

Preferably, said generation of a deteriorated color transform isobtained by reducing the bitdepth of the original color transform. Then,the second bit rate associated with the deteriorated color transform isinferior to the bitdepth of the original color transform.

In a first variant, said generation of a deteriorated image is obtainedby embedding said original image with said deteriorated color transform.

Preferably, said first bit rate associated with said deteriorated imageresults from an encoding of this deteriorated image.

In a second variant, said generation of a deteriorated image is obtainedby reducing the bitdepth of the original image. Then, the first bit rateassociated with the deteriorated image is inferior to the bitdepth ofthe original image.

A third aspect of the invention provides a system for embedding of atleast one original image with at least one original color transform,comprising:

an image generator configured to generate a deteriorated imageassociated with a first bit rate from at least said original image,

a color transform generator configured to generate a deteriorated colortransform associated with a second bit rate from at least said originalcolor transform,

means for applying said original color transform to said deterioratedimage resulting in a first test image,

means for applying said deteriorated color transform to said originalimage resulting in a second test image,

means for evaluating a first distortion by comparison of the first testimage with the original image,

means for evaluating a second distortion by comparison of the secondtest image with the original image,

means for evaluating a conjoint bit rate from a summation of the firstbit rate with the second bit rate,

means for evaluating a global distortion from a weighted summation ofthe first distortion with the second distortion,

means for determining the final conjoint bit rate associated with thebest trade-off when a predetermined trade-off between said conjoint bitrate and said global distortion is met,

means for choosing new values of said first bit rate and/or said secondbit rate such that a new conjoint bit rate evaluated from a summation ofthis new first bit rate with the new second bit rate is inferior to theprevious conjoint bit rate, when said predetermined trade-off is notmet,

means for redirecting to the image generator and to the color transformgenerator when said predetermined trade-off is not met, with said newfirst bit rate and said new second bit rate,

means for inferring the values of the final first bit rate and of thefinal second bit rate the summation of which corresponds to said finalconjoint bit rate when a predetermined trade-off between said conjointbit rate and said global distortion is met,

means for embedding the deteriorated image associated with this finalfirst bit rate with the deteriorated color transform associated withthis final second bit rate.

The advantages of embodiments of the invention are notably:

an optimization of image quality after color transformation, includingthe minimization of the distortion caused by embedding a colortransform.

an optimization of color transform precision, i.e. optimization of imagequality gained by applying the color transform.

a control of rate, as the invention can indicate explicitly how muchinformation of the image should be replaced—in the sense of informationtheory—by information related to the color transform in order to obtainan optimal quality.

BRIEF DESCRIPTION OF DRAWINGS

The invention will be more clearly understood on reading the descriptionwhich follows, given by way of non-limiting example and with referenceto the appended figures in which:

FIG. 1 is a diagram illustrating a method of embedding an original imagewith an original color transform according to a main embodiment of theinvention;

FIG. 2 is a diagram illustrating a first variant of the method shown onFIG. 1;

FIG. 3 is a diagram illustrating a second variant of the method shown onFIG. 1.

DESCRIPTION OF EMBODIMENTS

It will be appreciated by those skilled in the art that the diagramspresented on the figures represent conceptual views of illustrativecircuitry embodying the invention. It may be substantially representedin computer readable media and so executed by a computer or processor,whether or not such computer or processor is explicitly shown. Thefunctions of the various elements shown in the figures may be providedthrough the use of dedicated hardware as well as hardware capable ofexecuting software in association with appropriate software.

In a main non-limiting embodiment, the system used to implement theinvention comprises:

a server configured to provide original images and related originalcolor transforms, to process these original images and related originalcolor transforms into final deteriorated images and related finaldeteriorated color transforms, and to embed together these finaldeteriorated images and related final deteriorated color transforms,

a transmitter for transmitting the embedded final deteriorated imagesand related final deteriorated color transforms,

a terminal configured to receive the embedded final deteriorated imagesand related final deteriorated color transforms, and to apply eachreceived color transform on each associated received image in order tocolor transform this image.

The server includes any usual storing and processing means, as thosebased on a CPU connected through a bus to memories and usual peripheralsas a monitor. This server includes also software dedicated to theprocessing and to the embedding of images and related color transform.

The transmitter could be wireless, as for instance based on a Wi-Finetwork having a node included in the server and a node included in theterminal.

The terminal could be a gateway connected for instance to a TV set, orcould be a TV set itself. As the server, the terminal also includes atleast one processor configured to perform operations in accordance withembodiments of the invention

In a main non limiting embodiment of the method according to theinvention implemented, for example, on the above system and describedwith reference to FIG. 1, original images and related original CLUTsrepresenting color transforms are stored on the server.

Each original image comprises K pixels; the colors of each pixel areencoded into M color coordinates C(1) . . . C(M), wherein M is generallyequal to 3; each color coordinate is expressed in N bits, for instance 8bits. Therefore, the bit rate associated with each original image isK×M×N=R₀1.

Each original image is associated with an original color transform whichis adapted to transform the colors of this original image; a pluralityof original images are generally associated to the same original colortransform; this original color transform is represented by a colorlookup table—CLUT—having P entries, where each entry has for instance abit rate of Q bits. Then, the bit rate associated with the original CLUTis P×M×Q=R₀2.

For each original image stored on the server, a deteriorated imagehaving a first bit rate R1<R₀1 is generated, and/or, for the originalCLUT stored on the server and associated with this original image, adeteriorated CLUT having a second bit rate R2<R₀2 is generated. Suchgenerations are implemented on the server using dedicated software.

Then, when a deteriorated image is generated, this original CLUT isapplied to the deteriorated image resulting in a first test image, and,when a deteriorated CLUT is generated, this deteriorated CLUT is appliedto the original image resulting in a second test image. Suchapplications are implemented on the server using other dedicatedsoftware.

Then, using still other dedicated software, a first distortion dE1 iscalculated by comparison of the first test image with the originalimage, and a second distortion dE2 is calculated by comparison of thesecond test image with the original image. The distortions arecalculated as Peak Signal to Noise Rations (PSNR) such as described byDavid Salomon in his book entitled “Data Compression, The CompleteReference” 4th edition 2007, Springer. The first distortion dE1 allowsappreciating in how far the deterioration of the image—for instance byembedding of the CLUT with the image—reduces the image quality. Thesecond distortion dE2 allows appreciating in how far the deteriorationof the CLUT impacts on the image quality.

However, the compression data rate of the image and the resulting imagequality have to be taken into account, too. Therefore, a globaldistortion dE is calculated as a weighted summation of the firstdistortion dE1 with the second distortion dE2, and a conjoint bit rate Ris calculated as a summation of the first bit rate R1 with the secondbit rate R2.

The two distortions dE1 and dE2 are averaged giving dE=0.5 dE1+0.5 dE2assuming that both distortions are decorrelated. The averaging can alsobe weighted, for example dE=0.75 dE1+0.25 dE2, if image compressionquality is more important for a given application that image colorquality. This is useful since reduced compression quality leads tostructured noise while reduced color transform quality leads tospatially smooth color errors.

Then, a test is applied to determine if the global distortion dE and theconjoint bit rate R correspond to a predetermined trade-off or not.

This trade-off can be determined for example as follows. For example,when calculating first and second test image several times withdifferent rates for the color transform, a tradeoff between data rate Rand image quality dE can be analyzed and optimized for instance in thesense of the rate-distortion theory, i.e. looking for the lowest rate atlowest distortion. This is done for instance in the following way.First, from all calculations of dE and R, the largest value of dE, nameddEmax, and the largest value of R, named Rmax, are determined. Then oneof the calculations is chosen as the best such that(dE/dEmax−1)̂2+(R/Rmax−1)̂2 is maximum ensuring that the chosencalculation of dE, R is farthest away from the maximum (worst solution)in a normalized rate-distortion diagram. Such a choice of dE, Rcorresponds to a determined trade-off between data rate R and imagequality dE. Other way to determine a trade-off between data rate R andimage quality dE can be used to implement the invention.

If the predetermined trade-off is not met, new values of the first bitrate R′1 and/or of the second bit rate R′2 are chosen such that the newconjoint bit rate R′ evaluated from a summation of this new first bitrate R′1 with the new second bit rate R′2 is inferior to the previousconjoint bit rate R, and another loop of the previous steps above islaunched with this new first bit rate R′1 and/or this new second bitrate R′2, starting, as above, with the generation of a new deterioratedimage having this new first bit rate R′1 and/or a new deteriorated CLUThaving a new second bit rate R′2.

If the predetermined trade-off between the evaluated conjoint bit rate Rand the evaluated global distortion dE is met, then a final conjoint bitrate R_(f) associated with this trade-off is determined. Note that thefinal conjoint bit rate R_(f) may correspond to the conjoint bit rate R′of the last iteration or loop above, or may correspond to the conjointbit rate of a previous iteration as it may give a best trade-offcompared to the last iteration. In any case, this final conjoint bitrate R_(f) would correspond anyway to a conjoint bit rate of aniteration already performed, when it was associated in this iterationwith a value of a first bitrate and with a value of a second bitrate,which are then considered respectively as a final first bit rate R_(f)1and as a final second bit rate R_(f)2.

In the final step of the method of embedding, using known softwareembedding means included in the server, the deteriorated imageassociated with this final first bit rate R_(f)1 is embedded with thedeteriorated color transform associated with this final second bit rateR_(f)2. This deteriorated image is considered as the optimaldeteriorated image, and this deteriorated color transform is consideredas the optimal deteriorated color transform.

Then, the transmitter sends to the terminal the optimal deterioratedimage with the optimal deteriorated color transform as embeddedtogether.

When receiving the optimal deteriorated image together with the optimaldeteriorated CLUT, the terminal separates the optimal deteriorated imagefrom the optimal deteriorated CLUT, and applies the optimal deterioratedCLUT to the optimal deteriorated image in order to get a colortransformed image.

If the terminal is a gateway connected to a TV set, the terminal thensends the color transformed image to the TV set for display.

The advantages provided by embodiments of the invention are notably:

an optimization of image quality as displayed on the TV set, i.e. aftercolor transformation, including the minimization of the distortioncaused by embedding a color transform with the image for transmission.

an optimization of color transform precision, i.e. an optimization ofimage quality gained by applying the color transform.

a control of rate for the transmission, because the embedment isperformed through an optimization of the amount of information of theimage that can be replaced by information related to the colortransform.

The main embodiment of the method according to the invention can beimplemented more specifically according to different variants.

A first variant is illustrated on the diagram of FIG. 2 where only thebitdepth R2 of the deteriorated CLUT is reduced from one iteration ofthe process to the next one and where the bitdepth R1 of the image whichis deteriorated by compression is kept constant. In this variant, ateach iteration of the process, the deteriorated image results from theembedding of the corresponding deteriorated CLUT into the original imageand the bit rate R1 of this deteriorated image results from an encoding(compression) of this deteriorated image. Several compression principlescould be implemented for this encoding. If the well-known variablebitrate principle is used, an aimed distortion dE1_aim is defined andthe encoding process adapts itself to this requirement, resulting to abitrate R1 and to a distortion dE1 close to the aimed distortiondE1_aim. The aimed distortion depends on the application depending onimage content and bitrate constraints. If the fixed bitrate principle isused, R1 is fixed and given, while dE1 results from encoding such asshown in FIG. 2. The bitrate depends on the application. For example forHDTV images, a rate R1 of 1 MB/s is a good choice. Any other known dataencoding method can be used. After each iteration which does not passthe “trade-off” test above, another deteriorated CLUT associated with asecond bit rate R′2<R2 is generated, such that the bit rate R′2associated with this other deteriorated CLUT is inferior to R2, andthen, another iteration is launched until global distortion dE andconjoint bit rate R values are obtained that met the predeterminedtrade-off requirement of the test. Note that, if R1 is either invariantover all iterations (constant bitrate encoding principle) or comes outthe encoding process (variable bitrate encoding principle), thevariation R′−R of the conjoint bit rate from one iteration to a new onecorresponds to either the variation R′2−R2 of the second bit rate, or tothe variation R′2−R2+R′1−R1, respectively.

A second variant is illustrated on the diagram of FIG. 3. In thisvariant, at each iteration of the process:

the bit depth N of the color coordinates is reduced by one, resulting ina new bit depth N′=N−1. The bit depth R′1 for the generation of thedeteriorated image being equal to the product K×M×N′ is then reduced toone in comparison with the bit depth R1 of the previous iteration.

-   -   the bit depth Q of the entries of the CLUTs representing the        deteriorated color transforms is reduced by one, resulting in a        new bit depth Q′=Q−1. The bit depth R′2 for the generation of        the deteriorated CLUTs being equal to the product P×M×Q′ is then        reduced to one in comparison with the bit depth R2 of the        previous iteration.

Although the illustrative embodiments of the invention have beendescribed herein with reference to the accompanying drawings, it is tobe understood that the present invention is not limited to these preciseembodiments, and that various changes and modifications may be effectedtherein by one of ordinary skill in the pertinent art without departingfrom the invention. All such changes and modifications are intended tobe included within the scope of the present invention as set forth inthe appended claims.

It is to be understood that the invention may be implemented in variousforms of hardware, software, firmware, special purpose processors, orcombinations thereof. The invention may be notably implemented as acombination of hardware and software. Moreover, the software may beimplemented as an application program tangibly embodied on a programstorage unit. The application program may be uploaded to, and executedby, a machine comprising any suitable architecture.

1. Method of embedding at least one original image with at least oneoriginal color transform, comprising: A/ generation, from at least saidone original image, of a deteriorated image associated with a first bitrate, B/ generation, from at least said one original color transform, ofa deteriorated color transform associated with a second bit rate, C/application of said at least one original color transform to saiddeteriorated image to obtain a first test image, D/ application of saiddeteriorated color transform to said original image to obtain a secondtest image, E/ obtaining a first distortion by comparison of the firsttest image with the original image, F/ obtaining a second distortion bycomparison of the second test image with the original image, G/obtaining a conjoint bit rate from a summation of the first bit ratewith the second bit rate, H/ obtaining a global distortion from asummation of the first distortion with the second distortion, saidsummation being optionally weighted, then, a tradeoff between theconjoint bit rate and the global distortion being determined, in thecase where said trade-off is met, determining a final conjoint bit rateassociated with said trade-off, otherwise in the case where saidtrade-off is not met, selecting new values of said first bit rate and/orsaid second bit rate such that a new conjoint bit rate obtained from asummation of said new first bit rate, if any, or previous first bitrate, if no new first bit rate is selected, with said new second bitrate, if any, or previous second bit rate, if no new second bit rate isselected, is inferior to the previous conjoint bit rate, and repeating aloop of steps A/ to H/ with said new first bit rate and/or said newsecond bit rate, when said final conjoint bit rate associated with saidtrade-off is determined, inferring the values of the final first bitrate and of the final second bit rate such that the summation of thefinal first bit rate and of the final second bit rate corresponds tosaid final conjoint bit rate from a previous loop of steps A/ to H/, andembedding the at least one deteriorated image associated with said finalfirst bit rate from said previous loop with the deteriorated colortransform associated with said final second bit rate from the sameprevious loop.
 2. Method of embedding according to claim 1 wherein saidcolor transforms are Color Look Up Tables (CLUT).
 3. Method of embeddingaccording to claim 1 wherein said generation of a deteriorated colortransform is obtained by reducing the bitdepth of the original colortransform.
 4. Method of embedding according to claim 1 wherein saidgeneration of a deteriorated image is obtained by embedding saidoriginal image with said deteriorated color transform.
 5. Method ofembedding according to claim 4 wherein said first bit rate associatedwith said deteriorated image results from an encoding of saiddeteriorated image.
 6. Method of embedding according to claim 1 whereinsaid generation of a deteriorated image is obtained by reducing thebitdepth of the original image.
 7. System for embedding at least oneoriginal image with at least one original color transform, comprising:an image generator configured to generate, from at least said originalimage, a deteriorated image associated with a first bit rate, a colortransform generator configured to generate, from at least said originalcolor transform, a deteriorated color transform associated with a secondbit rate, a module configured to apply said original color transform tosaid deteriorated image resulting in a first test image, a moduleconfigured to apply said deteriorated color transform to said originalimage resulting in a second test image, a module configured to evaluatea first distortion by comparison of the first test image with theoriginal image, a module configured to evaluate a second distortion bycomparison of the second test image with the original image, a moduleconfigured to evaluate a conjoint bit rate from a summation of the firstbit rate with the second bit rate, a module configured to evaluate aglobal distortion from a weighted summation of the first distortion withthe second distortion, a module configured to determine the finalconjoint bit rate associated with the best trade-off when apredetermined trade-off between said conjoint bit rate and said globaldistortion is met, a module configured to select new values of saidfirst bit rate and/or said second bit rate such that a new conjoint bitrate evaluated from a summation of this new first bit rate with the newsecond bit rate is inferior to the previous conjoint bit rate, when saidpredetermined trade-off is not met, a module configured to redirect tothe image generator and to the color transform generator when saidpredetermined trade-off is not met, with said new first bit rate andsaid new second bit rate, a module configured to infer the values of thefinal first bit rate and of the final second bit rate the summation ofwhich corresponds to said final conjoint bit rate when a predeterminedtrade-off between said conjoint bit rate and said global distortion ismet, a module configured to embed the at least one deteriorated imageassociated with this final first bit rate with the at least onedeteriorated color transform associated with this final second bit rate.